Camera systems are widely used for various applications, particularly in the printing industry. For example, camera systems can be used for registration measuring systems, inspection systems or web monitoring systems. In many cases digital image sensors such as CCD cameras are employed as color cameras, whose light-sensitive pixels provide three output signals corresponding to the colors recorded in the observation area via three separate color channels, usually for the colors red, green and blue.
In connection with the known camera systems, a problem occurring during the inspection of colored printed products is that the color data provided by the color cameras often do not correspond to the color sense of the human eye. Unprocessed image data from these color cameras are unsatisfactory in the areas of color balance, brightness, contrast and reproduction of the color hue when compared to human color perception. Both optical devices and illumination devices have shortcomings and the spectral sensitivity distribution of CCD cameras exacerbates the color balance problems, brightness problems, contrast problems and color hue problems. The sensitivity distribution of the cameras used does not always agree with the sensitivity distribution of the human eye, and so the image data provided by the color camera makes a false visual impression during later processing, such as when viewed on a video display monitor.
A method for correcting image data by means of a correction matrix is disclosed in U.S. Pat. No. 5,189,511.
U.S. Pat. No. 4,930,009, U.S. Pat. No. 5,331,441 and U.S. Pat. No. 6,278,533 also disclose methods for correcting image data of a camera system with a color camera, using a correction matrix.